The present invention is a member for use in a door or window frame which is readily adjustable for installation in walls of varying thicknesses.
In common building construction door and window openings are usually rough framed with wooden studs. The studs are later covered on both sides by plaster, wall panels or more often by a gypsum-filled wallboard known in the building trade as "sheetrock". Studs average about 88.9 mm (3.5 in width). However, this dimension is not consistent between various parts of the country, or even from sawmill to sawmill. Gypsum board is sold in various thicknesses. Local building codes usually dictate the thicknesses that will be required at any given location in a building. The most common thickness is 12.7 mm (0.5 in), but a 15.9 mm (0.625 in) grade is almost as common. Not infrequently a wall will have one thickness on one face and a different thickness on the other face.
Varying wall thicknesses pose expensive problems. Door and window frames are almost invariably made of clear, knot-free lumber. Due to the scarcity of large trees from which clear lumber is cut, such lumber has become extremely expensive. Waste must be minimized. If wall openings were always of uniform thickness, suitable door and window frames could be cut in the sawmills. As it is, most carpenters must now start with wider boards and labor intensively to trim these to the desired finished width. This incurs a waste of both labor and of materials.
Various people in the past have addressed the problem of making frames which are adjustable in width for wall openings. Kelly, in U.S. Pat. No. 1,197,031, shows a two-part door jamb. Steps are milled in one part of this jamb and in the stop. The jamb portions can be moved relative to each other to accomodate wider or narrower openings, with any gap between them being covered by the stop. Shipway, in U.S. Pat. No. 2,185,650, shows a similar construction which is simpler in principle but, utlimately, is more complex in practice. The gap between a two-part jamb is covered with a stop member. The jamb portions are nailed to mounting brackets after they are adjusted as to width and the brackets are thereafter nailed to the studs defining the wall opening. Lester, Jr., in U.S. Pat. No. 2,651,814, shows a complex four-part door frame. The jamb is divided into two members and each member has a longitudinal slot along its interior edge. The stop has a T-shaped base which fits in the slots along the edges of the jamb. After the frame is installed, a second part of the stop is nailed adjacent the first in order to cover any gap created by adjustment during installation. Frydenburg, U.S. Pat. No. 3,707,057, shows a construction similar to that in the Lester patent. However, the stop is a plastic molding, similar to a hose, which can compress or expand as the jamb members are adjusted. Casebolt, et al., U.S. Pat. No. 3,553,891, shows a very complex adjustable jamb.
Adjustable jambs shown by Swanson, U.S. Pat. No. 3,800,488, and McAllister, U.S. Pat. No. 3,981,103, have somewhat more similarity to the one of the present invention. Swanson's frame is a two-piece foamed plastic molding. The stop is integral with one jamb piece and has a slot molded in the end to accomodate the other jamb piece. Because of the particular slot construction employed, this frame has a very small bearing area against the studs which define the door opening. McAllister's device is a complex integral frame and moldings. A vinyl covered wooden member is cut with a series of V-shaped kerfs which go all the way through the wood, but do not cut the vinyl skin. This is folded at the kerfs to form a two-piece structure of adjustable width. One jamb portion is held in place by a retainer piece nailed to the inside of the other jamb. This cooperates with the stop to form a slot in which the first jamb piece is fitted.
The construction shown in U.S. Pat. Nos. 1,197,031 and 3,981,103 both waste considerable portions of the wood. Because of their relative complexity it is doubtful whether any of the previously known adjustable frames really represent an economy over traditional methods of construction. The present invention has addressed that problem and is a major step forward.